U.S. patent application number 12/118623 was filed with the patent office on 2008-11-13 for method for the subsequent treatment of welded connections.
This patent application is currently assigned to GKSS-FORSCHUNGSZENTRUM GEESTCHACHT GMBH. Invention is credited to Frank Gartner, Thomas Klassen, Mustafa Kocak, Heinrich Kreye, Stefan Riekehr, Thorsten Stoltenhoff, Waman Vishwanath Vaidya.
Application Number | 20080277458 12/118623 |
Document ID | / |
Family ID | 39514641 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080277458 |
Kind Code |
A1 |
Kocak; Mustafa ; et
al. |
November 13, 2008 |
METHOD FOR THE SUBSEQUENT TREATMENT OF WELDED CONNECTIONS
Abstract
A method for the subsequent treatment of welded connections is
shown and described. The object of providing a method for the
subsequent treatment of a weld by which the tensile stresses in the
region of the weld are reduced is achieved by applying a top layer
to the weld on a workpiece by cold-gas spraying.
Inventors: |
Kocak; Mustafa; (Geesthacht,
DE) ; Riekehr; Stefan; (Geesthacht, DE) ;
Vaidya; Waman Vishwanath; (Geesthacht, DE) ; Gartner;
Frank; (Hamburg, DE) ; Stoltenhoff; Thorsten;
(Ennepetal, DE) ; Kreye; Heinrich; (Hamburg,
DE) ; Klassen; Thomas; (Wentorf, DE) |
Correspondence
Address: |
HOVEY WILLIAMS LLP
10801 Mastin Blvd., Suite 1000
Overland Park
KS
66210
US
|
Assignee: |
GKSS-FORSCHUNGSZENTRUM GEESTCHACHT
GMBH
Geesthacht
DE
|
Family ID: |
39514641 |
Appl. No.: |
12/118623 |
Filed: |
May 9, 2008 |
Current U.S.
Class: |
228/222 |
Current CPC
Class: |
C23C 24/04 20130101 |
Class at
Publication: |
228/222 |
International
Class: |
B23K 31/02 20060101
B23K031/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2007 |
DE |
102007021736.8 |
Claims
1. A method for the subsequent treatment of a weld on a workpiece,
said method comprising the steps of: providing the workpiece with
the weld; and applying a top layer to the surface of the weld by
cold-gas spraying.
2. The method as claimed in claim 1, said cold-gas sprayed top
layer being formed of particles lying between 10 and 60 .mu.m.
3. The method as claimed in claim 1, said workpiece comprising
aluminum or aluminum alloys.
4. The method as claimed in claim 1, said workpiece comprising
titanium or titanium alloys.
5. The method as claimed in claim 1, said workpiece comprising
steel.
6. The method as claimed in claim 5, said workpiece being provided
with a coating comprising zinc.
7. The method as claimed in claim 1, said workpiece comprising
copper or copper alloys.
8. The method as claimed in claim 1, said top layer comprising
material behaving anodically with respect to the material of the
weld.
9. The method as claimed in claim 1, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
10. The method as claimed in claim 8, said workpiece comprising an
aluminum alloy, said top layer consisting of aluminum.
11. The method as claimed in claim 10, said workpiece including a
coating of aluminum.
12. The method as claimed in claim 2, said particles lying between
20 and 45 .mu.m.
13. The method as claimed in claim 8, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
14. The method as claimed in claim 9, said workpiece comprising an
aluminum alloy, said top layer consisting of aluminum.
15. The method as claimed in claim 3, said top layer comprising
material behaving anodically with respect to the material of the
weld.
16. The method as claimed in claim 4, said top layer comprising
material behaving anodically with respect to the material of the
weld.
17. The method as claimed in claim 3, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
18. The method as claimed in claim 4, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
19. The method as claimed in claim 15, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
20. The method as claimed in claim 16, said top layer comprising
material behaving anodically with respect to the material of the
workpiece.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of and priority
from German Application No. DE 10 2007 021 736.8, filed May 9,
2007, the entire disclosure of which is hereby incorporated by
reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for the subsequent
treatment of a weld on a workpiece, in order to improve the
mechanical properties of the weld.
[0004] 2. Discussion of the Prior Art
[0005] In particular in the area of aircraft construction, where
aluminum is used to a very great extent, it is endeavored to
connect workpieces that consist of this material or its alloys to
one another by means of welds instead of by riveting, since this
has an accompanying weight saving, which is highly relevant
specifically in this area.
[0006] As in the case of all metals, it is also the case with
aluminum that, no matter which thermal welding method is chosen,
when producing a weld there is the problem that tensile stresses
occur in the material of the weld itself and in the material of the
adjacent workpieces in the region of the weld. These tensile
stresses may on the one hand lead to the strength of the material
being reduced. On the other hand, the tensile stresses may also
have the effect under loading that cracks form in the region of the
surface, further impairing the strength of the weld and
accelerating the corrosion in this region.
[0007] To overcome the problem of tensile stresses, it is possible
to anneal the welded workpieces, that is to say carry out a thermal
treatment. If, however, the workpieces exceed a certain size, such
treatment can no longer be carried out. Furthermore, with annealing
there is the problem that the workpieces may possibly be distorted
in the process, which is likewise undesired. Finally, subsequent
thermal treatment is ruled out in the case of materials that are
already hardened.
[0008] Furthermore, it proves to be a problem that the aluminum
workpieces that are to be welded often consist of an aluminum alloy
with a coating of pure aluminum, the coating serving as a
"sacrificial anode", in order to protect the aluminum alloy of the
workpiece from corrosion. In the region of the weld, this coating
is destroyed by the welding process, so that in this region the
effect of the sacrificial anode is also lost and the aluminum alloy
of the workpieces is more exposed here to corrosion attacks.
Furthermore, the region of the weld becomes more electronegative as
a result of mixing in of the material of the coating, and
consequently is at increased risk of corrosion. It would therefore
be desirable furthermore if, after the production of a weld on such
workpieces, a sacrificial anode material were also present once
again in the region of the weld.
SUMMARY
[0009] It is therefore the object of the present invention to
provide a method for the subsequent treatment of a weld by which
the tensile stresses in the region of the weld are reduced.
[0010] This object is achieved according to the invention by a top
layer being applied to the weld on a workpiece by cold-gas
spraying.
[0011] In this case, the weld may be formed before the application
of the top layer by any desired welding methods known from the
prior art, gas fusion welding, arc welding and laser welding coming
into consideration in particular. The weld may on the one hand
serve the purpose of connecting two components to form a single
workpiece, or on the other hand serve the purpose of closing
openings in a workpiece.
[0012] In the cold-gas spraying, powdered material from which the
top layer is formed is introduced into a gas jet inside a nozzle,
so that the particles are accelerated to high speeds, typically to
speeds above the speed of sound, and consequently high kinetic
energies are imparted to them. When the particles impinge on the
workpiece or the surface of the weld that is to be coated, they
form a dense, firmly adhering layer, since the high kinetic energy
and the resultant release of heat on impingement on the workpiece
cause the particles to bond together and also to the workpiece. For
details of cold-gas spraying, you are otherwise referred to German
Patent No. DE 101 26 100 A1, and corresponding U.S. Pat. No.
7,143,967, both of which are hereby incorporated by reference
herein in their entirety, to the extent not inconsistent with the
present disclosure.
[0013] Due to the constant impact of further solid particles,
cold-gas-sprayed layers have compressive stress after application
to a workpiece. Furthermore, compressive stresses are introduced
into the workpiece itself during the coating process.
[0014] This gives rise to the possibility of using the application
of a cold-gas-sprayed layer to the surface of a previously formed
weld to compensate for the tensile stresses in it, and consequently
increase the strength. In this way, the tendency for cracks to form
is also greatly reduced, so that in this way the corrosion
resistance of the weld is improved.
[0015] If the size of the particles used in the cold-gas spraying
lies between 10 and 60 .mu.m, and preferably between 20 and 45
.mu.m, it has been found that good results can be achieved with
regard to the reduction of tensile stresses in the weld and the
workpiece.
[0016] Even if the present invention is not restricted to
workpieces made of a material comprising aluminum or aluminum
alloys, the method according to the invention has proven to be
particularly advantageous with regard to such workpieces. However,
it is also possible for the method according to the invention to be
applied to workpieces made of titanium or titanium alloys. In
addition, the method according to the invention can be applied to
workpieces made of steel; in particular whenever galvanized steel
workpieces are subjected to subsequent treatment, it is possible to
restore the originally good corrosion properties in the region of
the weld. Furthermore, the method may also be applied to copper and
copper alloys.
[0017] To further improve the corrosion resistance of the weld, it
has proven to be advantageous if the material of the top layer
behaves anodically with respect to the material of the weld. In
this case, the top layer not only counteracts the tensile stresses,
but at the same time serves as a sacrificial anode with respect to
the weld, so that the material of the weld is not exposed to
corrosion attacks.
[0018] In a further preferred way, the material of the top layer
may also be chosen such that it behaves anodically with respect to
the material of the workpiece, and also consequently acts as a
sacrificial anode with respect to the latter. With such a choice of
the material of the top layer, it is possible in particular to
restore the properties that existed before the formation of the
weld, as long as the workpiece is provided with a coating formed as
a sacrificial anode.
[0019] In particular, the materials may be chosen in such a way
that the material of the workpieces comprises an aluminum alloy and
the top layer consists of aluminum, the workpieces in a further
preferred way also having a coating of aluminum.
[0020] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the detailed description of the preferred embodiments. This summary
is not intended to identify key features or essential features of
the claimed subject matter, nor is it intended to be used to limit
the scope of the claimed subject matter.
[0021] Various other aspects and advantages of the present
invention will be apparent from the following detailed description
of the preferred embodiments and the accompanying drawing
figures.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0022] The invention is described below on the basis of a drawing,
which merely represents a preferred exemplary embodiment and in
which:
[0023] FIG. 1 schematically shows the construction of a device for
carrying out the method according to the invention.
[0024] The drawing figures do not limit the present invention to
the specific embodiments disclosed and described herein. The
drawings are not necessarily to scale, emphasis instead being
placed upon clearly illustrating the principles of the preferred
embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The present invention is susceptible of embodiment in many
different forms. While the drawings illustrate, and the
specification describes, certain preferred embodiments of the
invention, it is to be understood that such disclosure is by way of
example only. There is no intent to limit the principles of the
present invention to the particular disclosed embodiments.
[0026] In FIG. 1, a workpiece 1 with a weld 3 is shown, it being
possible for the weld 3 to be formed by known welding methods, for
example gas fusion welding, arc welding and laser welding. The
material of the workpiece 1 in the preferred exemplary employment
described here is an aluminum alloy; a coating 5 of pure aluminum
is also present on the workpiece 1, serving as a sacrificial anode
and interrupted in the region of the weld 3 on account of the
welding process. In the example described here, the thickness of
the workpiece 1 may lie between 0.5 and 10 mm, and the coating 5
may be formed by multiple layers. In the case of the method
according to the invention, however, it is also conceivable to use
workpieces made of copper or titanium and also titanium or copper
alloys. However, it is also possible to use workpieces made of
steel; in particular whenever galvanized steel workpieces are
subjected to subsequent treatment, it is possible to restore the
originally good corrosion properties in the region of the weld.
[0027] On account of the welding process, the material of the weld
3 is formed from the material of the workpiece 1 itself and that of
the coating 5, and consequently becomes more electronegative than
the material of the workpiece. As a result, the weld 3 is initially
more susceptible to corrosion than the rest of the workpiece 1.
Furthermore, the weld 3 and the region of the workpiece 1 adjacent
to it are under tensile stresses before the coating, so that, as
explained at the beginning, the strength and the corrosion
resistance are reduced here (see arrows 7).
[0028] To carry out the method according to the invention, the
workpiece 1 is arranged at a distance of between 10 and 60 mm in
front of a cold-gas spray nozzle 9, which is only schematically
represented here.
[0029] In the cold-gas spray nozzle 9, particles with a size of
between 10 and 60 .mu.m, and preferably between 20 and 45 .mu.m,
are accelerated typically to speeds above the speed of sound in a
gas jet 11. The material of the particles in the present exemplary
embodiment is aluminum, and nitrogen is used as the process gas, it
being possible for the process gas to be preheated and the process
gas being at a pressure of between 5 and 60 bar, with preference
between 20 and 40 bar.
[0030] The particles in the gas jet 9 impinge on the workpiece 1 in
the region of the weld 3 and form a top layer 13 over the weld 3.
In this case, the gas jet 9 has a typical diameter of from 2 to 10
mm, so that, with preference, the region of the weld 3 is passed
over repeatedly in lines, in order to apply the top layer 13 of
pure aluminum to the region of the weld 3 with a thickness of from
0.05 to 10 mm.
[0031] Applying the top layer 13 to the weld 5 in the way according
to the invention by means of cold-gas spraying has the effect that
the particles bond together in the top layer 13 and to the
workpiece 1 on account of the high kinetic energy of the particles
and the resultant release of heat on impingement on the workpiece
1. Furthermore, at the beginning of the coating process,
compressive stresses are introduced into the workpiece 1 itself,
thereby compensating for tensile stresses 7 that are present after
the welding. After that, compressive stresses (arrow 15) are built
up in the top layer 13, due in part to the constant impact of
further solid particles.
[0032] This gives rise to the possibility of using the application
of a cold-gas-sprayed top layer 13 to the surface of a previously
formed weld 3 to compensate for the tensile stresses 7 in it, and
consequently increase the strength. In this way, the tendency for
cracks to form is also greatly reduced, so that in this way the
corrosion resistance of the weld 3 is improved.
[0033] Since the top layer 13 consists of pure aluminum in the
preferred exemplary embodiment described here, the top layer 13
behaves anodically both with respect to the workpieces 1 and with
respect to the weld 3, so that in this way the corrosion resistance
of the welded workpiece is improved.
[0034] The preferred forms of the invention described above are to
be used as illustration only, and should not be utilized in a
limiting sense in interpreting the scope of the present invention.
Obvious modifications to the exemplary embodiments, as hereinabove
set forth, could be readily made by those skilled in the art
without departing from the spirit of the present invention.
[0035] The inventors hereby state their intent to rely on the
Doctrine of Equivalents to determine and access the reasonably fair
scope of the present invention as pertains to any apparatus not
materially departing from but outside the literal scope of the
invention set forth in the following claims.
* * * * *